Filter

ABSTRACT

Aerosol filters, particularly cigarette filters, are formed from short synthetic fibers containing a bonding agent by confining a random array of said fibers having an orientation predominantly transverse to the longitudinal axis of said filter in an area having the desired configuration and activating the bonding agent to form a coherent article.

United States Patent Roberts et a1. 1451 Apr. 18, 1972 [54] FILTER3,225,390 12/1965 Kistler ..l3l/26l X [72] Inventors: John D. Roberts;John D. Ellenberg; 3,313,665 4/1967. Berger ..13l/268 X Charles, Kefih aofchafloue N C 3,364,938 1/1968 Mumpower et al... ..131/269 X 3,444,8635/ 1969 Soehngen et a1 ..131/266 X [73] Assignee: Celanese Corporation,New York, NY.

FOREIGN PATENTS OR APPLICATIONS [22] F11ed: Nov. 13, 1968 757,841 9/1956Great Br1ta1n ..l31/267 [21] App]. No.: 775,390

' Primary Examiner-Samuel Koren 52 us. (:1 ..l3l/267, 131/268, 131/269AssismmE-\'aminerl- 51 Int. Cl. ..A24b 15/02, A24d 01/04, A24f07/04 o-Morgan, Stephen p y and William [58] Field of Search ..131/268, 267,266, 264, 261, M350" 131/66, 66 A, 64, 64 A, 84, 84 A, 8,10,10.7, 10.9,

84 B [57] ABSTRACT Aerosol filters, particularly cigarette filters, areformed from [56] References C'ted short synthetic fibers containing abonding agent by confining UNITED STATES PATENTS a random array of saidfibers having an orientation predominantly transverse to thelongitudinal axis of said filter in an 3,552,400 1 971 Berger et a1"131/267 X area having the desired configuration and activating thebond- Hackney et al. 1 3 agent to form a coherent article 3,050,4308/1962 Gallagher ..13 l/268 UX 3,068,873 12/1962 Allman, Jr. et a]...131/l0.7 3 Claims, 2 Drawing Figures HEATED COOLING VACUUM FLUIDHEATED FLUID PATENTEDMH 18 I972 13, 656,484

INVENI ORS JOHN D. ROBERTS JOHN D. ELLENBERG CHARLE H. KEITH FIG. I.

FILTER SUMMARY OF THE INVENTION The present invention relates generallyto the formation of aerosol filters, and more particularly to cigarettefilters. Briefly, the cigarette filters of the present inventioncomprise a substantially cylindrical rod comprised of short syntheticfibers bonded at their points of contact with one another by a suitablebonding agent. The arrangement of the fibers within said rod may bedescribed as random with the exception that the fibers are predominantlylengthwise oriented in a primarily vertical plane.

The filters of the present invention are preferably formed by dispersinga plurality of short fibers associated with a latent bonding agent intoa rapidly flowing, preferably turbulent, air stream, sweeping saidfibers in said air stream into a cylindrical zone to form a rodconforming to the interior dimensions of said zone, confining saidfibers in the cylindrical configuration by wrapping a porous belt aboutthe rod as it exits from said zone in order to transport said rodthrough succeeding processing zones, removing air from the confinedfibers, heating the rod to activate the bonding agent therein and form acoherent structure, cooling the coherent structure, removing the beltfrom about the coherent structure, treating the surface of the coherentstructure to remove irregularities therefrom, and cutting the coherentstructure to the desired length.

DRAWING FIG. 1 is a side view of the apparatus described in thespecification.

FIG. 2 is a cross-sectional view of a cigarette filter showing thetransversely oriented fibers.

DETAILED DESCRIPTION OF THE DRAWING Aerosol filters, particularlycigarette filters, have conventionally been produced from corrugatedsheets of paper or from synthetic continuous filament tows in which thefilaments are generally aligned with the longitudinal axis of thefilter. While other techniques, such as baffles, etc. have beenattempted, only the paper filters and filters of continuous syntheticfilaments, particularly-cellulose acetate, have met with any widecommercial acceptance.

Paper filters are generally characterized by a higher filtration asmeasured by smoke removal efiiciency at a given pressure drop, butsuffer the disadvantage of adversely affecting taste and odor of thedelivered smoke stream. Moreover, the phenol selectivity of paperfilters is generally significantly lower than that available withconventional tow filters. Also, paper filters are susceptible tocollapse during smoking, whereby the filter medium may become separatedfrom the containing wrapper, permitting the smoke to channel about themedium and arrive at the smokers mouth essentially unfiltered.

On the other hand, tow filters, particularly bonded cellulose acetatetow filters, are more successful in selectively removing phenols, andgenerally exhibit acceptable compressibility, i.e., resistance tolateral deformation, but would desirably exhibit enhanced smoke removalefiiciencies without loss in organoleptic quality of the delivered smokestream.

Accordingly, the principal object of this invention is to provide anaerosol filter especially adapted for the filtration of tobacco smoke,characterized by high filtration efficiency, suitable compressibility,and an aesthetically acceptible delivered smoke stream.

In accordance with the primary teachings of this invention, there isprovided a gas filter consisting essentially of discrete fiber elementsbonded at random points of contact therebetween into a structure whereinthe predominant orientation of the fibers is transverse to the gasstream path.

Generally, the present filters may be characterized as being of lowerweight and improved compressibility at equivalent pressure drop andsmoke removal efficiency in comparison with conventional continuousfilament tow filters.

While the theory of smoke filtration has not been thoroughly elucidated,many studies point to an impact phenomenon as extremely significant. Itis postulated, without limitation arising therefrom, that theimprovement in filtration afforded by the filters of this inventionresides at least in part in the transverse orientation of the fiberelements, increasing the probability of impact with the particulatematter in the aerosol stream.

The desirability of fiber orientation normal to the axis of thecigarette filter plug has not gone unnoticed in the art, but each of theprior suggestions have proven unworkable in practice. Thus, U.S. Pat.No, 2,855,937 describes a structure used by disposing fibers verticallyon a paper wrapper and then forming a cylindrical rod therefrom whereinthe fibers intermesh" with each other and are directed toward a commoncenter. While this construction provides transverse orientation of thefiber elements, it will be seen by inspection that the concept requiresa cross section having a variable density. Accordingly, the concentratedmass of interrneshed fibers at the common center tends to force thesmoke to the periphery of the plug where a relatively low density of themedium is available to act on the smoke stream. Acceptablecompressibility, as well as the construction methods, necessitate astiff wrapper, and production techniques are extremely critical.

Allman et al., in U.S. Pat. No. 3,068,873 also describes a filterstructure containing transversely oriented fiber segments, theindividual segments thereof containing no internal free fiber ends whichmay interact to form a coherent continuous filter rod, adapted tohandling in a commercial cigarettemaking operation.

U.S. Pat. No. 3,225,390 emphasizes the desirability of increasing thetransverse orientation of loose fibrous material in filter plugs toenhance the lateral strength thereof, and discloses formation of plugsfrom a web having about 25 percent to 50 percent of the fibers thereinoriented in a direction 30 of the perpendicular to the axis of the plugbeing formed. The desired effect on filtration efficiency resulting fromthis limited reorientation of fiber elements is necessarily minimal,which is also the failing of some other suggested approaches, such asthose of U.S. Pat. Nos. 2,805,671 and 3,033,212.

It will be seen from the foregoing discussion that while thedesirability of transversely oriented fiber elements in a cigarette plugmay have been appreciated, no acceptable product having a high order oftransverse orientation has heretofore been developed, and no process isavailable whereby such products may be uniformly and continuouslymanufactured on a commercial scale.

Accordingly, a further and more specific object of the present inventionis a provision of a cigarette filter rod having a uniformcross-sectional density, a high order of resistance to lateralcompression even without any wrapping material, and sufficientlongitudinal coherency or structural integrity to permit handling insubsequent processing of relatively long lengths thereof withoutsplitting or cracking. Another major object of the invention is theprovision of an uncomplicated and economical process for manufacturingthe aforesaid filters in a continuous, high-speed, commercial scale. Astill further object is to provide a manufacturing line utilizingequipment especially adapted to afiect the process for making suchfilters.

Still other objects of the present invention, if not specifically setforth herein, will become apparent to one skilled in the art upon areading of the following detailed description of the invention taken inconjunction with the drawing.

Essentially, the filters of the present invention are prepared fromshort fibers of approximately 0.5 mm. to 8 mm., and preferably 1 mm. toabout 3 mm. in length. For the sake of convenience, these fibers will bereferred to herein as flock.

The flock utilized in the preferred embodiment of the present inventionis prepared from filamentary materials which preferably comprise organicderivatives of cellulose such as esters or ethers thereof, e.g.,cellulose organic acid esters such as cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose benzoate, cellulose acetateformate, cellulose acetate propionate, cellulose acetate butyrate, andthe like, and ethers such as ethyl cellulose etc. The esters may beripened and acetone-soluble, such as conventional cellulose acetate, ormay be substantially fully esterified, i.e., contain fewer than 0.29free hydroxyl groups per anhydroglucose unit, such as cellulosetriacetate.

In preparing this flock, continuous filaments are spun from a suitablespinnerette of conventional design, taken up into a raw tow of a typewell known in the cigarette filtration art, and packaged, preferably ina bale. The continuous filament tow may then, optionally, but notnecessarily, be removed from the bale and passed through a conventionalbanding jet and a subsequent opening means which serves to deregisterthe crimps in the filaments. This portion of the process is more fullydescribed and a suitable device for performing this operation is shown,for example, in U.S. Pat. No. 3,156,0l6. After deregistration of thecrimped tow, the tow may be passed through a means for applying asuitable plasticizer and/or adhesive bonding agent thereto. A suitableapplicator for this purpose is shown, for example, in Us. Pat. No.3,387,992. Other applicators such as wick applicators or jet spray meansmay be utilized for this purpose. The plasticized tow is then passedthrough a cutting device which severs the tow into the desired lengths.As an alternative, the tow may be cut into short lengths prior toapplication of the plasticizer, and the plasticizer may then be sprayedonto or otherwise applied to the chopped fibers. For example, theplasticizer may be mixed with the fibers as they are in the turbulentstream jet prior to rod formation.

Plasticized short fibers thus prepared are then passed into a holdingbin or other suitable container, or may be passed directly into theapparatus of the present invention.

In the preferred embodiment of the present invention, flock prepared inthe manner described above is passed to a feed loop 12. The feed loop 12conducts a rapidly moving stream of flock past the opening oftube 14.The flock is then blown into tube 14 which terminates within housing 16.Flock blown into nonporous tube 14 is compacted into rod form with theindividual fibers being predominantly aligned in a transverse direction.This transverse alignment is attributable to formation within thenonporous tube and the presence of preceding fibers which serve as animpact barrier.

As the flock, now in the shape of a cylindrical rod exits from tube 14,a continuous porous belt 18, preferably a woven nylon or Teflon coatedfiberglass belt, is wrapped around the exiting mass of flock to confinethe flock into the cylindrical rod configuration produced by tube 14.Belt 18 is threaded around pulleys 20 and 22, at least one of whichprovides a rotary motion to belt -18. As the belt and encased flockexits from housing 16, it passes through a vacuum chamber 24 which isemployed to create an area of vacuum used to draw the flock into tube14. Chamber 24 is to be considered optional since the air stream alonemay be sufficient to convey the flock into tube 14.

Thereafter, the belt and rod pass through a section of tubing 26 whichacts as a pressure drop area to prevent fluid injected in subsequentoperations from being withdrawn by vacuum chamber 24.

After tube 26, the flock and belt pass through heating chambers 28 and30 wherein the flock is subjected to a heated fluid which activates thebonding agent within the flock to produce bonding between the individualfibers and create a coherent cylindrical structure.

In the drawing and the preferred embodiment of the present invention,the heating chamber is shown as a two-part device. In the portiondesignated as 28, the heated fluid is passed downwardly through theflock and in portion 30 the heated fluid is passed upwardly through theflock. In this manner, both sides of the flock are uniformly heated toobtain uniform bonding. Of course, it will be understood, that it isonly preferred that the two segments inject fluid into the cylindricalmaterial from substantially opposite directions, and need not bepositioned such that the heating fluid flows downwardly in one segmentand upwardly through the other. The preferred fluid in the presentinvention is heated air. However, other gases or steam may be employedwith equally desirable results.

After heat activation of the bonding agent, the flock is passed into acooling chamber to complete bonding. This chamber, like the heatingchamber, is a two-part device designated in the drawings as 32 and 34.In this portion of the apparatus, cool air is passed in one directionthrough the flock in the first segment of the cooling chamber and in theopposite direction in the second segment of the cooling chamber.Thereafter, the flock and porous belt exit from the cooling chambers 32and 34 and the porous belt is then opened from about the coherentcylinder of flock and rotates around pulley 22 to return to the initialphase of the operation. The coherent bonded rod 36 extruded from theoperation then passes through a skinner device 38. The skinner device 38is preferably a Teflon coated gland having a heating source around theopening therein. Passing of the rod through skinner 38 serves to removethe longitudinal seam created by belt 18 from the surface of the rod, aswell as any other surface irregularities. After removal of surfaceirregularities by passing of the rod 36 through skinner 38, rod 36 isthen passed to a cutter 40 which is timed to sever rod 36 into thedesired lengths.

It is to be understood that the preceding description is of thepreferred embodiment of the present invention and that manymodifications are possible. For example, a dielectric heater may be usedinstead of a heated fluid. Also, the cooling chamber may be eliminatedand the rods stored for a period of time to insure satisfactory bonding.

While the preferred embodiment has been described in conjunction withcellulose acetate flock having thereon as a bonding agent, e.g.,triacetin, it will be understood by one skilled in the art that flockmay be prepared from other fiber-forming polymers. Examples of suitablepolymers are the polyamides such as nylon, polyesters such aspolyethylene terephthalate, polyglycolic acid and copolymers thereof,acrylonitrile polymers and copolymers, polymers and copolymers of olefinand vinyl esters such as ethylene, propylene, vinyl chloride, vinylidenechloride, vinyl acetate, and the like.

The preferred plasticizer used in conjunction with the the preferredcellulose ester fibers of the present invention is triacetin. However,other suitable plasticizers such as dibutyl phthalate, ethyl glycolate,triethyl citrate, polyalkylene glycols and esters thereof, or the likemay be employed. It will also be understood by the skilled artisan thata suitable plasticizer or adhesive bonding agent may be employed whenusing other of the above described fiber sources.

It is also within the scope of the present invention to add otherfiltration materials to the flock prior to filter formation, e.g., byaddition of such materials to the rapidly moving air stream along withthe flock. Particularly suitable materials include activated carbon,alumina, silica gel, diatomaceous earth, and other high surface areasolids. In addition, additives such as wood pulp and non-bonded fibersmay be employed. Generally, these additives will be used in amount offrom about 2 to about 50 percent of the total weight of the filter andmore preferably from about 5 to about 20 percent of the total weight. Itis to be understood, of course, that the amount employed will depend toa degree upon the particular additive being used.

Preferably, the fibers described herein will have a dpf i.e., denier perfilament of from about 0.5 to about 25, and even more preferably fromabout 1.0 to about 5. With a dpf much above 5, there is a sacrifice infiltration performance. Because of the structure of the present filter,it is possible to utilize lower dpf fibers without a sacrifice in thecompressibility, i.e., resistance to lateral deformation, than hasheretofore been experienced in utilizing these lower dpf fibers.

While the present filters have sufficient structural rigidity tofunction without a supporting wrapping, it is within the scope of thepresent invention to use additional wrappings about the filters, ifdesired.

An additional advantage of the present filter is its relatively lightweight. For example, filters prepared inaccordance with the proceduredescribed herein need weigh only about 60-80 percent (exclusive ofwrapping) as much as conventional acetate tow filters havingsatisfactory pressure drop (resistance to draw) and S.R.E. (smokeremoval efficiency). At the same time, this light weight does notdetract from desirable filtration. To illustrate, present filters of 20mm in length and 8 mm. in diameter, having a pressure drop of about20-90 mm. of water weigh about 0.08 to about 0.14 gram and have a smokeremoval efficiency of about 25 to about 55 percent. In comparison,conventional cellulose acetate tow filters within this pressure drop andS.R.E. range have a weight of fiber and plasticizer of about 0. 11 toabout 0.16 gram.

Compressibility, i.e., resistance to lateral deformation, of the hereindescribed filter is also superior to that of a conventional celluloseacetate tow filter. Conventional tow filters having the above pressuredrop, S.R.E. and dimensions have a compressibility of about 30 to about55 percent. On the other hand, comparable present filters have acompressibility of only about 5 to about 30 percent. In other words, thecompressibility of the present filter is about 15 'to about 55 percentof the compressibility of the conventional cellulose acetate tow filtersof comparable size and pressure drop and S.R.E.

The above values have compressibility which was obtained using a TMlprecision dead-weight micrometer manual Model 551 manufactured byTesting Machines, Inc., Mineola, NY. compressibility was determined bymeasuring the initial diameter of the rod with a micrometer, dropping a300 gram weight on the rod from a height of 0.425 inches and reading thecompressed diameter of the rod after the weight had come to rest.Percent compressibility was then calculated from these figures.

It is to be understood that the above values were preferred filtershaving properties within the commercially acceptable ranges. Of course,one may also prepare filters of even lighter weight or further improvedcompressibility by following the teachings of the present invention.

The above superior properties of the present filters are felt to beattributable primarily to the fiber orientation in the filter structure.Testing has shown that approximately 40 to 60 percent of the fibers arealigned within 10 to the perpendicular of the filter axis. Also, thefibers are substantially uniformly disposed across the filter crosssection.

The above data on fiber orientation was determined by taking micronslices across a filter and cutting strips of 100 microns in width fromthe filter slice. All the fibers in the section were first counted. Thenall fibers having a length greater than 100 microns, i.e., allsubstantially perpendicular fibers, were counted. From these figures thepercent of substantially perpendicular fiberswere calculated.Substantial uniformity across the filter section was determined bytaking samples at various angles and comparing the variations in resultsobtained in thetest procedure, the variation observed to be only minor.

The following example is presented for the sake of illustration only,and should not be construed as being in limitation of the presentinvention.

' EXAMPLE Filters of 8mm in diameter and 20mm. in length we. preparedfrom fibers of 2 mm. in length and the dpf noted below using thepreviously described apparatus and process.

The noted properties were determined and are compared withconventionally prepared cellulose acetate filters.

While the preceding description has emphasized the utility of thepresent invention in conjunction with aerosol filters, other uses suchas tampons, wicks, felt-tipped" pens, packing material, etc., will beobvious to the skilled artisan.

It will be apparent to one skilled in the art that many modificationsand variations of the hereinbefore described invention are possible.

What we claim is:

l. A cigarette filter comprising a mass of fibers, the majority of saidfibers consisting essentially of very short thermoplastic fibers havinga length from about 1 mm. to substantially less than 3 mm. and bonded attheir points of contact, 40 to 60 percent of said fibers being alignedwithin at least i 10 percent of the perpendicular of the axis of saidfilter and substantially uniformly disposed across the cross section ofthe filter, said filter when being approximately 8 mm. in diameter and20 mm. in length exhibiting a pressure drop of 20 to mm. of water, asmoke removal efficiency of from about 25 to about 55 percent, a weightof from about 0.08 to about 0. l4 grams, and a compressibility of fromabout 5 to about 30 percent.

2. The cigarette filter of claim 1 wherein said fibers are celluloseacetate fibers.

3. The cigarette filter of claim 1 wherein said fibers have a denier perfilament of from about 1 to about 5.

2. The cigarette filter of claim 1 wherein said fibers are celluloseacetate fibers.
 3. The cigarette filter of claim 1 wherein said fibershave a denier per filament of from about 1 to about 5.